ESTRO 2021 Abstract Book

S493

ESTRO 2021

progression-free interval (R-PFI), OS, and local progression-free interval (L-PFI) were estimated using Kaplan- Meier method and compared using the log-rank test. Results Fifty-one patients with 84 BM received SRT and IT. The patients were mostly men (60.8%) and WHO 1 (56.9%). For SRT, most lesions were treated with either 15 to 21 Gy in a single fraction (56.0%); or with 18 to 27 Gy in three fractions (41.8%). For IT, patients were treated with Nivolumab (47.1%), Pembrolizumab (33.3%), Durvalumab (15.7%), or Atezolizumab (3.9%) for a median duration of 4.9 months. Among lesions, 76 (90.5%) were intact, and eight (9.5%) were previously resected. The median follow-up from SRT was 22.5 months (2.7– 47.3). Six- months and 1-year R-PFI in “SRT before IT” group, “concurrent SRT and IT” group, and “SRT after IT” group were 24.1% and 24.1% vs 56.3% and 49.6% vs 41.0% and 34,2% respectively, (p=0.094). Although no significant difference has been observed in R-PFI, there was a trend in better regional control of BM from NSCLC in the ‘‘concurrent SRT and IT” group. One-year OS was 67.5% vs 70.2% vs 69.2%, respectively (p= 0.44). One- year L-PFI was 70.1% vs 78.9% vs 77.8%, respectively (p= 0.79). There was no difference in toxicity between the three groups regarding radionecrosis or acute neurological toxicity. Conclusion Regional control of BM from NSCLC seems to be better in the ‘‘concurrent SRT and IT” group without an increase in acute neurological toxicity or radionecrosis rate. These results may lead to prospective studies on larger cohorts. OC-0629 A hypoxia-immune prognostic classifier for head-and-neck cancer patients undergoing radiotherapy N. Nicolay 1,2 , A. Rühle 1 , M. Mix 3 , N. Wiedenmann 1 , R. Stoian 1 , G. Niedermann 1 , D. Baltas 1 , M. Werner 4 , J. Ruf 3 , G. Kayser 4 , A. Grosu 1,2 1 University Medical Center Freiburg, Radiation Oncology, Freiburg, Germany; 2 German Cancer Consortium, Partner Site Freiburg, Heidelberg, Germany; 3 University Medical Center Freiburg, Nuclear Medicine, Freiburg, Germany; 4 University Medical Center Freiburg, Surgical Pathology, Freiburg, Germany Purpose or Objective High levels of tumor-infiltrating lymphocytes (TILs) result in favorable outcomes of head-and-neck squamous cell cancer (HNSCC) patients after radiotherapy, and TIL levels are influenced by the tumor microenvironment and tumor-associated hypoxia. The present analysis from a prospective imaging trial investigated the value of combining TIL and tumor hypoxia data to derive an immune hypoxia prognostic classifier for HNSCC patients. Materials and Methods 49 patients with locoregionally advanced HNSCCs were enrolled in this prospective imaging trial and received repeat hypoxia PET/CT imaging with fluoro-18 misonidazole ([18F]FMISO) in weeks 0, 2 and 5 during chemoradiation. Tumor-associated hypoxia was defined as a tumor-to-background SUV above 1.4, and early hypoxia response was assumed for a decrease in the normalized maximum intratumoral SUV (FMISO-T/B index ) between weeks 0 and 2. TILs and the hypoxia tissue marker carbonic anhydrase IX (CAIX) were analyzed in pre- therapeutic tissue specimens. Patients were stratified into subgroups according to TIL numbers (>100 vs. <100 TILs/HPF) and PET-based early hypoxia response (response vs. no response), and the resulting classifier was internally validated based on TIL numbers and CAIX expression (above vs. below median H-score). Locoregional control (LRC) and progression-free survival (PFS) were assessed for all subgroups using Cox and concordance analyses (Harrell’s C). Results High TIL levels corresponded to better LRC (HR=0.279, p =0.011) and PFS (HR=0.276, p =0.006). Similarly, a decrease in the FMISO-T/B index between weeks 0 and 2 correlated with improved LRC (HR=0.321, p =0.015) and PFS (HR=0.402, p =0.043). Harrell’s C was 0.68 for a combination of TIL and early hypoxia response values. The hypoxia PET-based hypoxia-immune classifier separated 3 distinct prognostic HNSCC patient subgroups: a favorable (TIL high / early PET response), an intermediate (TIL high /no early PET response or TIL low /early PET response) and a poor (TIL low /no early PET response) prognostic group with a 2-year LRC of 71%, 33% and 0%, respectively. Low tissue levels of CAIX also correlated with improved LRC (HR=0.352, p =0.050) but not PFS (HR=0,468, p =0,087). Harrell’s C was 0.66 for CAIX expression and TILs separately and 0.71 for the combination. The immunohistochemistry-based immune-hypoxia classifier similarly stratified between a favorable (CAIX low /TIL high ), an intermediate (CAIX low /TIL low or CAIX high /TIL high ) and a poor (CAIX high /TIL low ) subgroup with 2-year LRC rates amounting to 73%, 62% and 11%, respectively. Conclusion We developed a hypoxia PET-based hypoxia-immune classifier that was able to stratify HNSCC patients into 3 distinct prognostic subgroups based on their tumor biology. These subgroups could also be separated with a clinically feasible, immunohistochemistry-based classifier with comparable model accuracy. This hypoxia- immune classifier could help to stratify prognoses of HNSCC patients undergoing radiotherapy pending validation in an external cohort. OC-0630 Olaparib combined with radiotherapy for TNBC: 1-year toxicity report of the RADIOPARP phase 1 trial P. Loap 1 , D. Loirat 2 , F. Berger 3 , M. Rodrigues 2 , L. Bazire 1 , J. Pierga 2 , F. Ricci 4 , K. Cao 1 , A. Vincent-Salomon 5 , F. Laki 6 , C. Ezzili 3 , A. Jochem 3 , L. Raizonville 3 , V. Mosseri 3 , M. Ezzalfani 3 , A. Fourquet 1 , Y. Kirova 1 1 Institut Curie, Department of Radiation Oncology, Paris, France; 2 Institut Curie, Department of Medical Oncology, Paris, France; 3 Institut Curie, Department of Statistics, Paris, France; 4 Institut Curie, Clinical Investigation Unit, Paris, France; 5 Institut Curie, Department of Pathology, Paris, France; 6 Institut Curie, Department of Surgery, Paris, France

Purpose or Objective